Ultramicrotome diamond knife

ABSTRACT

An ultramicrotome diamond tool is provided with a diamond knife blade having first and second planar surfaces which intersect to define a cutting edge and a shank for holding the knife blade. In one embodiment of the ultramicrotome diamond tool the cutting edge of the blade is defined by the intersection of naturally occurring (111) and (100) crystal planes and is primarily usable in materials science and machine tool applications. In a second embodiment of the ultramicrotome diamond tool, the cutting edge of the blade is defined by the intersection of naturally occurring (320) and (111) crystal planes and is primarily usable in biological science applications to cut biological tissue or the like. The blade is usable to cut a material specimen that has a longitudinal axis and that is being advanced in a direction along its longitudinal axis toward the ultramicrotome tool. The blade is mounted on a shank having a longitudinal axis. The shank is mounted on a base to cause the longitudinal axis of the shank to be substantially orthogonal to the longitudinal axis of the material specimen.

This invention relates to ultramicrotome diamond tools and particularlyto a diamond tool blade having a cutting edge at the intersection of twonaturally occurring crystal planes within the diamond structure of theblade.

Ultramicrotome diamond tools are used to slice very thin sections from amaterial specimen such as biological tissue to provide a thin specimenfor study under a scanning or transmission electron microscope. Thesetools are also used in the materials science art to cut plastics,metals, or the like.

The chief problem encountered during the operation of a conventionalultramicrotome diamond tool or knife is "chatter". Chatter is the rapidvibration of the knife blade with respect to the material specimencausing the knife blade to cut the specimen unevenly. A materialspecimen is frequently irreparably damaged or spoiled if it has beensliced by a chattering knife blade. One cause of chatter is an unsharpor easily dulled knife blade cutting edge. A less than sharp knife bladewill bind as it cuts through the material specimen to produce anunclean, wavy cut. Another cause of chatter is exposure of the knifeblade to an external vibration. For example, a shop floor may transmitvibrations caused by a seismic wave or by operation of a forklift truckor the like to cause a conventional ultramicrotome diamond knife bladeto vibrate in an unwanted manner while a material specimen is being cut.Such an unwanted vibration deleteriously affects the plane of the cut byunpredictably changing the position of the cutting edge relative to thematerial specimen. Destruction of a non-replaceable material specimen orrepetition of a time-consuming cutting operation are two disadvantageouseffects of knife blade chatter.

One type of conventional ultramicrotome diamond knife is illustrated inFIGS. 1 and 2. FIG. 1 shows an idealized cubic-type diamond crystal 10with eight exposed octahedral faces 12. Each octahedral face 12 iscoincident with a naturally occurring (111) crystal plane of the diamondcrystal 10. This style of diamond crystal is typically used as a basefrom which all types of diamond tools are constructed. A diamondplatelet 14 is manually cleaved from the diamond crystal 10 by anexperienced gem cutter. The platelet 14 is cleaved along a (111) crystalplane (defined by broken lines in FIG. 1) parallel to the outwardlypresented octahedral face 14.

Two steps are required to transform the platelet 14 into a diamond knifeblade 16 of the type shown in FIG. 2. First, the triangle-shapedplatelet 14 is "squared-up" to form a rectangular parallelepiped (notshown) having mutually parallel (111) crystal planar faces 18 and 20.Second, the "squared-up" platelet 14 is machined to include facets 22and 24. A conventional cutting edge 26 is defined by the intersection offacets 22 and 24. Typically, facets 22 and 24 cooperate to define adihedral included angle of about 40° to 50° therebetween. Theconventional blade 16 shown in FIG. 2 is easily identified by itscharacteristic cross-sectional "roof-top" shape.

In the past, diamond platelets such as platelet 14 were never machinedor polished directly on a naturally occurring crystal plane such as the(111) plane because it was difficult to identify the location of thoseplanes and not economical to do so once such a plane was identified.Instead, gem cutters machined the platelet 14 six or seven degrees offof the (111) plane as shown in FIG. 2 and obtained the characteristic"roof-top" shape. Typically, the diamond platelet is fully cut andprepared before it is mounted on a shank. It is difficult toconsistently identify and cut along a crystal plane within acceptabletolerances using such a standard technique.

Experienced gem cutters are able to identify a (111) "three-point"crystal plane and a (100) "four-point" crystal plane by theircharacteristic symmetry. However, many other crystal planes such as a(320) plane are not so easily identified. Identification of such planeswould permit exploitation of many combinations of cutting-edge definingplanes not known in the prior art. One object of the present inventionis to identify and machine diamonds on crystallographic planes to obtaina sharper and stronger cutting edge that is less susceptible to"chatter".

The conventional diamond knife blade 16 is mounted in a metal shank 28to provide a conventional diamond knife assembly 30. The knife assembly30 is usable to slice a material specimen 32. Typically, a conventionalmaterial specimen 32 is movable in directions 34 and 36 in relation tofixed knife assembly 30. Specimen 32 is indexable in direction 34 to liein proximity to cutting edge 26 and reciprocable in direction 36 tocontact cutting edge 26 such that a very thin section 38 of the materialspecimen 32 is sliced with each downward stroke of the specimen 32. Thefixed knife assembly 30 is oriented such that its longitudinal axis 40is rotated at an angle 42 of about 20° to 30° with respect to thevertical 44. Canting of the shank 28 to maintain such an orientation isa contributing cause of chatter. This typical orientation further causesfacet 22 to be orthogonal to the axial direction 34 along which thematerial specimen 32 is incrementally indexed.

Conventional ultramicrotome diamond tools do not perform well undernormal operating conditions due to loss of cutting edge sharpness anddue to the susceptability of conventional blade-holding shanks toexternal vibration. According to the present invention, an improvedultramicrotome diamond tool including a blade faceted substantiallyalong naturally-occurring crystal planes to create a sharper andstronger cutting edge and including a vertically upright blade-holdingshank to better resist the influence of external vibrations minimizes"chatter" and advantageously avoids the shortcomings of conventionalultramicrotome diamond knives.

In accordance with the present invention, an ultramicrotome diamond toolor knife includes a knife blade having first and second naturallyoccurring planar surfaces which intersect to define a cutting edge and ashank for holding the knife blade. The blade is made by first cutting a(111) plane and then cutting along a second naturally occurring crystalplane at an acute angle in relation to the (111) plane. Thus, a blade ofthe present invention has a characteristic "wedge" shape and not the"roof-top" shape of conventional diamond knife blades.

The present invention advantageously reduces the unwanted effects ofknife blade chatter by causing the cutting edge of the diamond tool tobe substantially at the intersection of two naturally occurring crystalplanes of a diamond or other similar cubic crystalline structure. Itwill be understood that both natural and artificially manufactured gemsor crystals have naturally occurring crystal planes.

According to one illustrative embodiment, the first planar surface issubstantially coplanar with a (111) crystal plane and the second planarsurface is substantially coplanar with a (100) crystal plane. The firstand second planar surfaces intersect to define a dihedral angle of about54.7°. This first embodiment of the ultramicrotome tool is primarilyusable in materials science and machine tool applications to cut amaterial such as copper or ceramic. The knife blade is brazed into amilled cutout in the shank so that the (111) crystal plane presents aforwardly-facing vertically upright blade surface and the (100) crystalplane presents a upwardly-facing blade surface. Thus, the sharper andstronger cutting edge of the blade in the first embodiment of theultramicrotome diamond tool is defined by the intersection of naturallyoccurring (111) and (100) crystal plane.

According to another illustrative embodiment of the present invention,the first planar surface is substantially coplanar with a (320) crystalplane and a second planar surface is substantially coplanar with a (111)crystal plane. The first and second planar surfaces intersect to definea dihedral angle of about 36.8°. In contrast to the first embodiment,the second embodiment of the ultramicrotome tool is primarily usable inbiological science applications to cut biological tissue or the like.The blade is brazed into an end milled slot in the shank so that the(320) crystal plane presents a forwardly-facing, vertically uprightblade surface and the (111) crystal plane presents an upwardly-facingblade surface. Thus, the sharper and stronger cutting edge of the bladein the second embodiment of the ultramicrotome diamond tool is definedby the intersection of naturally occurring (320) and (111) crystalplanes.

The ultramicrotome diamond tool of the present invention is fixed innovel relation to a movable material specimen to be cut. The materialspecimen has a longitudinal axis. The material specimen is advanced in adirection along its longitudinal axis toward the ultramicrotome toolusing conventional techniques. The shank has a longitudinal axis and isfixed on a base so that the longitudinal axis of the shank issubstantially orthogonal to the longitudinal axis of the materialspecimen. Thus, the shank is fixed on its base in a novel substantiallyvertical upright orientation shown in FIGS. 5 and 7 rather than in theconventional canted orientation shown in FIG. 2. Such an upright shankorientation advantageously reduces the deleterious effects of knifeblade chatter and is a significant improvement over conventional knifeblade assemblies.

The invention can best be understood by referring to the followingdescription and accompanying drawings which illustrate preferredembodiments exemplifying the best mode of carrying out the invention aspresently perceived. In the drawings:

FIG. 1 is a perspective view of an octahedral diamond crystal showing a(111) plane along which the crystal may be cleaved to obtain atriangular platelet;

FIG. 2 is a diagramatic side elevation view of a conventional diamondtool or knife having a cutting edge defined by the intersection of twonon-naturally occurring crystal planes, the fixed knife being shown inproximity to a movable material specimen to be sliced;

FIG. 3 is a front view of a platelet mounted in a first type of shankaccording to the present invention;

FIG. 4 is a side elevation view of the platelet and shank shown in FIG.3 showing the platelet and shank to be severable along a dotted line toprovide a first embodiment of an ultramicrotome diamond tool accordingto the present invention;

FIG. 5 is a side elevation view of a first embodiment of anultramicrotome diamond tool according to the present invention showing acutting edge defined by the intersection of a (111) and a (100) crystalplane in proximity to a movable material specimen to be sliced;

FIG. 6 is a perspective view of a platelet mounted in a second type ofshank according to the present invention;

FIG. 7 is a side elevation of a second embodiment of an ultramicrotomediamond tool according to the present invention showing a cutting edgedefined by the intersection of a (320) and a (111) plane in proximity toa movable material specimen to be sliced;

FIG. 8 is a perspective view of a portion of a diamond crystal latticestructure showing a (111) and a (100) crystal plane;

FIG. 9 is a transverse cross-sectional view of the diamond crystalstructure shown in FIG. 8 taken along line 9--9 showing a cutting edgedefined by the intersection of the (111) and (100) crystal planes;

FIG. 10 is a perspective view of a portion of a diamond crystal latticestructure showing a (320) and a (111) crystal plane;

FIG. 11 is a transverse cross-sectional view of the diamond crystalstructure shown in FIG. 10 taken along line 11--11 showing a cuttingedge defined by the intersection of the (320) and (111) crystal planes;and

FIG. 12 is a diagramatic top view of a rotatable platter forcontinuously applying a composition to a mounted diamond to machine andpolish the diamond.

An ultramicrotome diamond tool or knife of the present inventionincludes a cutting edge defined by the intersection of two substantiallynaturally occurring planar surfaces of a natural or artificiallymanufactured cubic crystalline structure such as a diamond. Millerindicies are used to identify each family of crystal planes.

One embodiment of an ultramicrotome diamond tool exploits the angularrelationship between naturally occurring (111) and (100) crystal planes,is suitable for use in the materials science art, and is illustrated inFIGS. 3, 4, 5, 8, and 9. A second embodiment of an ultramicrotomediamond tool exploits the angular relationship between naturallyoccurring (320) and (111) crystal planes, is suitable for use in thebiological science art, and is illustrated in FIGS. 6, 7, 10, and 11. Itis known that a particular angular relationship may be required for onetool application and a slightly different angular relationship may berequired for another tool application. The angular relationships betweenmost pairs of intersecting crystal planes are obtainable in knownreference sources. Thus, the use of other pairs or combinations ofnaturally occurring crystal planes in an ultramicrotome diamond tool isalso within the scope of and contemplated by the present invention.

Both embodiments of the novel diamond tool advantageously reduce"chatter" by providing cutting edges that keep their sharpness over alonger period of time than conventional diamond tools. This advantage isobtained because at least one of the planar surfaces used to define thecutting edge of the diamond tool is substantially co-planar with anaturally occurring crystal plane. Further, a blade-holding shank ofnovel construction is used in each embodiment to better support thediamond blade in relation to a material specimen to be cut tosignificantly reduce "chatter."

Referring now to FIG. 5, a first embodiment of the present inventionincludes a first diamond tool 50 having a diamond blade 52 mounted on ashank 54. The shank 54 of the diamond tool is rigidly mounted on a base55 by conventional means to position the diamond blade 52 in proximityto an advancing material specimen 56 to be cut. The longitudinal axis ofthe mounted shank is substantially perpendicular to the longitudinalaxis of the advancing material specimen. The material specimen 56 ismovable relative to the diamond blade 52 in axial and radial directionsby any conventional technique such as thermoexpansion of a specimencarrying metal bar (not shown). Diamond blade 52 includes a cutting edge58 defined by the intersection of two naturally occurring crystalplanes. In particular, a (111) and a (100) plane have been selectedsince the dihedral angle between those planes is known to be 54.7°. Thatknown angle is very close to the 50° included angle that is the commonand standard cutting edge angle in the materials science field. Thiscutting edge angle is suitable for cutting plastic materials, ceramics,bones, and teeth.

The novel process for making and mounting diamond blade 52 issequentially illustrated in FIGS. 1, 3, 4, and 5. An octahedrally-shapeddiamond 10 is first notched and then cleaved along substantially a (111)crystal plane using conventional techniques to provide a standardtriangularly-shaped diamond platelet 14. An octahedral face of any cubiccrystalline structure such as diamond, silicon, germanium, and the likeis always in the (111) family of crystal planes. A diamond crystal willusually break along a (111) crystal plane when cleaved due to theexistence of very weak Carbon-to-Carbon bonds between such planesproduced by nitrogen segregation to the (111) crystal plane.

The (111) plane is identified by a plurality of little "etch pit"triangular surfaces made visible with a 500×eyepiece microscope byetching platelet 14 in a molten bath of potassium nitrate or other salt.Cleaved platelet 14 is first polished and then placed in the molten saltsolution to reveal the edge pit triangles illustrated in FIG. 3. Diamondplatelet 14 can be transformed into diamond blade 52 once a planesubstantially coplanar with the (111) plane has been obtained and theplatelet 14 has been mounted in a milled circular cut-out 60 in one endof shank 54 as shown in FIGS. 3 and 4. Shank 54 can be made of stainlesssteel, titanium, or the like. The circular cut-out 60 can be formed withan end mill to include a circular side wall 62 and a bottom wall 64. Oneof the two substantially parallel (111) planes of platelet 14 is placedagainst bottom wall 64 and the periphery of the diamond platelet 14 isbrazed to the metal shank 54 as shown in FIG. 4. The other of the twosubstantially parallel (111) planes of platelet 14 faces outwardly fromcut-out 60 upon completion of the mounting and brazing operations.

Diamond blade 52 is fabricated in a three step process. First, theexposed face 111 is polished in accordance with a novel machining andpolishing operation described below. Second, the metal shank 54 and themounted diamond platelet 14 are severed substantially along a planerepresented by broken line 66 in FIG. 4 in accordance with conventionalsevering techniques. The object of this "roughing" operation is toobtain a plane in close proximity to a naturally occurring (100) crystalplane. As mentioned above the dihedral included angle between (111) and(100) crystal planes is 54.7°. Desirably, the dihedral included anglebetween the exposed planar face 111 and the severed plane 66 is aboutthree or four degrees greater than the dihedral included angle betweenthe two intersecting naturally occurring crystal planes. This is becausethe diamond material immediately below the surface of plane 66 will becharacterized by unwanted material fatigue. This fatigued material cansubsequently be removed to expose a desired diamond crystal plane.Finally, the novel machining and polishing is performed on the severedplatelet 14 mounted on metal shank 14 to remove the proper amount ofdiamond material to expose face 100 of diamond blade 52 a finally shownin FIG. 5. Face 100 is substantially co-planar with a naturallyoccurring (100) crystal plane and intersects face 111 to define cuttingedge 58 of the diamond blade 52. This novel technique removes thefatigued material produced by the "roughing" operation without causingfurther material fatigue.

Standard diamond machining techniques are usable to perform theabove-described severing operation on metal shank 54 and diamondplatelet 14. For example, use of either a grinding wheel or a chargedscaife would be satisfactory. A diamond grinding wheel typicallycomprises a metal matrix wheel on which diamond grit is bonded by anepoxy. The wheel is similar to a regular grinding wheel; however, it hasdiamond powders. Further, the wheel is constantly washed in water orsolution to keep the metal from sticking and galling to the wheelitself. A charged scaife is a rotating platter. The scaife is chargedwith a mixture of oil such as whale or olive oil and diamond powderdripped thereon. The scaife has little pores to trap diamond powdertherein. This trapped diamond powder is usable to abrasively machine ametal-diamond article such as shank 54 and platelet 14. More metalmaterial than diamond material will be removed using either techniquesince the metal is a comparatively softer material. Thus, the metalshank 54 is ground to a lower level than the diamond platelet 14 toexpose plane 66. This "elevated" plane 66 is then available for furthermachining and polishing using the novel technique taught below.

A machining and polishing operation is now performed on the severedplatelet 14 mounted on metal shank 54. The machining and polishingoperation is also usable to polish the face 111 and is desirably carriedout partially in accordance with the teaching of U.S. Pat. No. 4,328,646and further in accordance with the novel process of the presentinvention.

The '646 patent discloses how to make a silicon oxide composition thatis usable in the novel manner described below to lap or polish themounted diamond platelet 14 along plane 66. Such a lapping operationremoves diamond material by removing selected carbon atoms that arebonded to the diamond crystal on an atom-by-atom basis. This type oflapping operation ultimately furnishes a diamond facet with anatomically smooth surface exhibiting little or no material fatigue belowthe surface in contrast to the material fatigue caused by theabove-described severing or "roughing" operation. Other conventionalmethods use grinding techniques which remove whole segments of material,create unwanted vibration in the diamond crystal, and significantlydamage the crystal structure of the diamond. The lapping operation iscontinued until a sufficient amount of diamond material has been removedto expose an ultrasmooth second planar face 100 which is substantiallycoplanar with a (100) crystal plane. Second planar face 100 intersectsplanar face 111 to define cutting edge 58 of diamond blade 52.

The machining and polishing operation may additionally be carried out inaccordance with the teaching of U.S. Pat. No 4,104,832. The '832 patentdiscloses how to form a deep coarse-pitched groove in a lapping disc toenable portions of the disc to lap the shoulders of a diamond stylus.The '832 patent discloses a rotatable lapping disc formed to include ahelical groove for engaging the tip of a stylus.

Referring now to FIG. 12, a lapping disc, slap or scaife 70 according tothe present invention is shown for continuously machining and polishingthe mounted diamond platelet 14 shown in FIG. 4 until a sufficientquantity of carbon atoms have been plucked out of the diamond crystal toexpose the planar face 100. The scaife 70 can be made out of ahigh-silicon, high carbon steel of the type used to polish and honechromium piston rings. The scaife 70 can have a flat diamond machiningsurface as shown in FIG. 12 or it can be formed to include a circulargroove similar to the groove shown in the '832 patent for engaging andmachining a diamond.

The scaife 70 is rotatable by drive means (not shown) and operablewithin a bell jar (not shown). The bell jar (not shown) surrounding thescaife 70 is divided into two adjacent portions by a pressure isolationbridge 72. A first pressure is caused to exist in a first portion 74,and a selected second pressure greater than the first pressure is causedto exist in a second portion 76. A vacuum is desirably pulled in firstportion 74. A "machining" gas such as Oxygen, Argon, N₂ O, or the likeis introduced into second portion 76.

The above described pressure system uses a differentially pumped seal onthe isolation bridge to permit a different pressure to exist in both thefirst and second portions. This is a common technique employed in vacuumcoating large sheets of glass, plastic film, or any other applicationinvolving moving parts and requiring a vacuum on one side andatmospheric pressure on the other side.

Scaife 70 is continuously operated in the following manner to machine adiamond such as diamond platelet 14 or any other hard, brittle material.First, a machining compound 78 such as the silicon oxide compositiondisclosed in the '646 patent is continuously deposited on the rotatablescaife 70 in first portion 74 using plasma deposition techniques.Second, a diamond platelet 14 or other material to be machined ismounted on a mounting fixture 80 in second portion 76 in proximity tothe scaife 70. Mounting fixture 80 is movable to selectively cause theplatelet 14 housed in second portion 76 to contact the machiningcompound 78 deposited on the rotatable scaife 70 in first portion 74.Carbon atoms are continuously removed from mounted platelet 14 untilsuch contact with the machining compound 78 is ceased. The platelet 14is machined in this fashion until the proper planar face 100corresponding to the (100) plane (for the first embodiment of thediamond tool) is exposed. Of course, the platelet 14 could also bemachined to obtain a different included angle should a naturallyoccurring crystal plane other than the (100) crystal plane be selected.At this point, the plane 66 and the underlying fatigued diamond materialhas been worn away by machining compound 78. The remaining planar face100 is substantially coplanar with a naturally occurring (100) crystalplane and is distinguished by its lack of material fatigue.

Scaife 70 is desirably fabricated to include a machining or workingsurface on its flat top 82 and also on its edge 84. The mounting fixture80 is movable to cause the crystalline structure mounted thereon tocontact either the flat top working surface 82 or the edge workingsurface 84. As mentioned previously, a groove may be formed in flat top82 to machine the mounted diamond to a particular edge radius orconfiguration. The diamond or crystalline structure is "polished" oncontact with flat top 82 and is "sliced" on contact with edge 84.

The crystal structure of a diamond that has been machined and polishedin the manner described above to obtain a diamond blade 52 having acutting edge 58 is illustrated in FIGS. 8 and 9. Thus, FIGS. 8 and 9show a first embodiment of an ultramicrotome diamond tool in which thecutting edge 58 is defined by the intersection of a (111) crystal planeand a (100) crystal plane. A diamond crystal includes a plurality ofcarbon atoms 90, each carbon atom 90 being covalently bonded (as notedby bonds 92) to four other carbon atoms located at the corners of aregular tetrahedron Each carbon atom 90 is shown to include four cubicfaces 94 and eight octahedral faces 96. As illustrated in FIGS. 8 and 9,a (111) crystal plane is defined by at least two octahedral faces 96 anda (100) crystal plane is defined by at least two cubic faces 94.

Referring now to FIG. 7, a second embodiment of the present inventionincludes a second diamond tool 150 having a diamond blade 152 mounted ona shank 154. The shank 154 of the diamond tool is rigidly mounted to abase 155 by conventional means to position the diamond blade inproximity to an advancing material specimen 156 to be cut. Diamond blade152 includes a cutting edge 158 defined by the intersection of twonaturally occurring crystal planes. In particular, (320) and (111)planes have been selected since the dihedral angle between those planesis 36.8° and close to the 40° included angle that is the common andstandard cutting edge angle in the biological science field. Thiscutting edge angle is suitable for cutting leathers, kidneys, biologicalspecimens, and plant sections.

The novel process for making and mounting diamond blade 152 issequentially illustrated in FIGS. 1, 6, and 7. The process issubstantially similar to the process described above in relation to afirst embodiment shown in FIG. 5. In this second embodiment, a diamondplatelet 14 is mounted in an elongated slot 161 milled in one end ofshank 154 as shown in FIGS. 6 and 7. The elongated slot 161 can beformed with an end mill to include a rectangular side wall 163 and arectangular bottom wall 165. One of the two substantially parallel (111)planes of platelet 14 is placed against side wall 163 and the peripheryof diamond platelet 14 is brazed to the metal shank 154 as shown in FIG.7. The other of the two substantially parallel (111) planes of platelet14 faces outwardly form side wall 163 upon completion of the mountingand brazing operations.

The metal shank 154 and the mounted diamond platelet 14 are severedsubstantially along a plane represented by broken line 166. Once again,the object of this severing operation is to obtain a plane in closeproximity to a naturally occurring crystal plane. However, in thisembodiment a (320) plane is ultimately sought rather than the (100)plane sought in the first embodiment.

The above-described novel machining and polishing operation of thepresent invention is now performed on the severed platelet 14 mounted onmetal shank 154 to remove the proper amount of diamond material toexpose face 320 of diamond blade 152 as shown in FIG. 7. Face 320 issubstantially coplanar with a naturally occurring (320) crystal plane.Planar face 320 intersects planar face 111' to define cutting edge 158of diamond blade 152.

The crystal structure of a diamond that has been machined and polishedto obtain a diamond blade 152 having a cutting edge 158 is illustratedin FIGS. 10 and 11. Thus, FIGS. 10 and 11 show a second embodiment of anultramicrotome diamond tool in which the cutting edge 158 is defined bythe intersection of a (320) crystal plane and a (111) crystal plane. Asillustrated in FIGS. 10 and 11, a (111) crystal plane is defined by atleast two octahedral faces 96 and a (320) crystal plane is defined by aplane including the common boundary 98 of two contiguous octahedralfaces 96.

Although the invention has been described in detail with reference tocertain preferred embodiments and specific examples, variations andmodifications exist within the scope and spirit of the invention asdescribed and defined in the following claims.

What is claimed is:
 1. An ultramicrotome diamond knife comprisingadiamond knife blade including first and second surfaces intersecting todefine a cutting edge, the first surface being substantially coplanarwith a first naturally occurring crystal plane within the crystallinestructure of the diamond, and the second surface being substantiallycoplanar with a second naturally occurring crystal plane within thecrystalline structure of the diamond.
 2. The ultramicrotome diamondknife of claim 1 wherein the first surface of the diamond knife bladeand a (111) crystal plane are substantially coplanar.
 3. Theultramicrotome diamond knife of claim 1 wherein the second surface ofthe diamond knife blade and a (100) crystal plane of the diamond knifeblade are substantially coplanar.
 4. The ultramicrotome diamond knife ofclaim 1 wherein the first surface of the diamond knife blade and a (320)crystal plane of the diamond knife blade are substantially coplanar. 5.The ultramicrotome diamond knife of claim 1 wherein the second planarsurface of the diamond knife blade and a (111) crystal plane of thediamond knife blade are substantially coplanar.
 6. The ultramicrotomediamond knife of claim 1 wherein the first and second surfaces intersectto define a dihedral included angle of about 30° to 45°.
 7. Theultramicrotome diamond knife of claim 1 wherein the first and secondplanar surfaces intersect to define a dihedral included angle of about45° to 60°.